Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

(LOSS) EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Calculation of basic and diluted earnings per share:
Antidilutive shares									3,519,159	2,961,439
Net (loss) income	$ (21,208)	$ (36,260)	$ (53,044)	$ (291,220)	$ (12,504)	$ 7,172	$ 8,068	$ 1,400	$ (401,732)	$ 4,136	$ 54,299
Net (loss) income attributable to noncontrolling interests									63,048	(1,352)	(17,787)
Net (loss) income attributable to Select Energy Services, Inc.	$ (17,983)	$ (30,541)	$ (44,298)	$ (245,862)	$ (9,930)	$ 5,379	$ 6,200	$ 1,135	(338,684)	2,784	36,512
Add: Reallocation of net income attributable to noncontrolling interests for the dilutive effect of performance share units										2
Add: Reallocation of net income attributable to noncontrolling interests for the dilutive effect of restricted stock										7	13
Add: Reallocation of net loss (income) attributable to noncontrolling interests for the dilutive effect of stock options										1	30
Net (loss) income attributable to Select Energy Services, Inc. - diluted									(338,684)	2,794	36,555
Class A Common Stock
Calculation of basic and diluted earnings per share:
Net (loss) income attributable to Select Energy Services, Inc.									(338,684)	2,784	35,720
Add: Reallocation of net income attributable to noncontrolling interests for the dilutive effect of performance share units										2
Add: Reallocation of net income attributable to noncontrolling interests for the dilutive effect of restricted stock										7	13
Add: Reallocation of net loss (income) attributable to noncontrolling interests for the dilutive effect of stock options										1	30
Net (loss) income attributable to Select Energy Services, Inc. - diluted									$ (338,684)	$ 2,794	$ 35,763
Weighted-average shares of common stock outstanding - basic									85,158,764	80,176,323	72,403,318
Dilutive effect of restricted stock										373,366	71,718
Dilutive effect of performance share units										80,979
Dilutive effect of stock options										40,215	166,999
Dilutive effect of ESPP										446	112
Weighted-average shares of common stock outstanding - diluted									85,158,764	80,671,329	72,642,147
Earnings (loss) per share, Basic (in dollars per share)									$ (3.98)	$ 0.03	$ 0.49
Earnings (loss) per share, Diluted (in dollars per share)									$ (3.98)	$ 0.03	$ 0.49
Class A-2 Common Stock
Calculation of basic and diluted earnings per share:
Net (loss) income attributable to Select Energy Services, Inc.											$ 792
Net (loss) income attributable to Select Energy Services, Inc. - diluted											$ 792
Weighted-average shares of common stock outstanding - basic											1,604,575
Weighted-average shares of common stock outstanding - diluted											1,604,575
Earnings (loss) per share, Basic (in dollars per share)											$ 0.49
Earnings (loss) per share, Diluted (in dollars per share)											$ 0.49
Class B Common Stock
Calculation of basic and diluted earnings per share:
Weighted-average shares of common stock outstanding - basic									16,221,101	23,806,646	31,986,438
Weighted-average shares of common stock outstanding - diluted									16,221,101	23,806,646	31,986,438